P4554 Xiaoming game

Each point is connected to the edge point, it is next to the same dis 0, 1 is different.

n = 3, m = 3 for each reference point as follows:

1 2 3

4 5 6

7 8 9

Such unique arrangement starting reference, numerals calculated $ (i-1) * m + j $, even at the boundary side is determined, because the topics from the default coordinate (0,0) starts, it is convenient to do title, the read 1 and end point are added. Then run a shortest path on it

#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
using namespace std;
int n,m;
int ex,ey,px,py;
int a[505][505];
char ch[255];

struct node{
    int to,nxt,dis;
}e[20000005];
int head[250005],cnt,dis[250005],in[250005];
inline void add(int from,int to,int dis){
    e[++cnt]=(node){to,head[from],dis};
    head[from]=cnt;
}
void spfa(){
    queue<int>q;
    for(int i=1;i<=n*m;++i)
        dis[i]=2000000000,in[i]=0;
    dis[(ex-1)*m+ey]=0;
    in[(ex-1)*m+ey]=1;
    q.push((ex-1)*m+ey);
    while(!q.empty()){
        int now=q.front();
        q.pop();
        in[now]=0;
        for(int i=head[now];i;i=e[i].nxt)
            if(dis[now]+e[i].dis<dis[e[i].to]){
                dis[e[i].to]=dis[now]+e[i].dis;
                if(!in[e[i].to]){
                    q.push(e[i].to);
                    in[e[i].to]=1;
                }
            }
    }
    printf("%d\n",dis[(px-1)*m+py]);
}
int main(){
    while(scanf("%d%d",&n,&m)){
        if(n==0&&m==0)break;
        cnt=0;
        memset(head,0,sizeof(head));
        for(int i=1;i<=n;++i){
            scanf("%s",ch+1);
            for(int j=1;j<=m;++j){
                if(ch[j]=='@')a[i][j]=1;
                else a[i][j]=0;
            }    
        }
        for(int i=1;i<=n;++i)
            for(int j=1;j<=m;++j){
                if(i>1)
                    add((i-1)*m+j,(i-2)*m+j,a[i][j]^a[i-1][j]),add((i-2)*m+j,(i-1)*m+j,a[i][j]^a[i-1][j]);
                if(i<n)
                    add((i-1)*m+j,i*m+j,a[i][j]^a[i+1][j]),add(i*m+j,(i-1)*m+j,a[i][j]^a[i+1][j]);
                if(j>1)
                    add((i-1)*m+j,(i-1)*m+j-1,a[i][j]^a[i][j-1]),add((i-1)*m+j-1,(i-1)*m+j,a[i][j]^a[i][j-1]);
                if(j<m)
                    add((i-1)*m+j,(i-1)*m+j+1,a[i][j]^a[i][j+1]),add((i-1)*m+j+1,(i-1)*m+j,a[i][j]^a[i][j+1]);
            }
        scanf("%d%d%d%d",&ex,&ey,&px,&py);
        ex++;ey++;px++;py++;
        spfa();
    }
    return 0;
}